Evidence of recent lateral gene transfer among hyperthermophilic Archaea

A total of 153 nucleotide differences were found over a contiguous 16 Wb re gion between two hyperthermophilic Archaea, Pyrococcus furiosus and Thermoc occus litoralis. The 16 kb region in P. furiosus is flanked by insertion se quence (IS) elements with inverted and direct repeats. Both IS elements con tain a single open reading frame (ORF) encoding a putative protein of 233 a mino acids identified as a transposase, This 16 kb region has the features of a typical bacterial composite transposon and represents a possible mecha nism for lateral gene transfer between Archaea or possibly between Archaea and Bacteria. A total of 23 homologous IS elements was found in the genome sequence of P. furiosus, whereas no full-length IS elements were identified in the genomes of Pyrococcus abyssi and Pyrococcus horikoshii. Only one IS element was found in T. litoralis. In P. furiosus and T. litoralis, the 16 kb region contains an ABC transport system for maltose end trehalose that was characterized biochemically for T. litoralis. Regulation of expression studies showed that the maIE gene, located on the transposon, and the encod ed trehalose/maltose-binding protein (TMBP) are induced in the presence of maltose and trehalose in both P. furiosus and T. litoralis. The implication s of transposition as a mechanism for lateral gene transfer among Archaea a re discussed.